Abstract: This paper studies the optimum way to design both type and position of the stiffeners when a steel bridge is assembled by means of the new protect-patented launching method based on a self-supporting deck system. This procedure is able to launch bridge up to a span of 150 m, in an economical and sustainable way. The main objective of this research paper is to numerically analyze the best stiffener combination and distribution along the length of bridge, both longitudinally and transversally, in order to avoid the patch-loading phenomenon in the slender webs. An optimum design of a triangular cell along the lower plate is also presented. Thus the best stiffener distribution along the deck can be achieved to solve the two most important factors during the launching of a steel bridge: the huge forces on the support section – higher than the serviceability limit state – and buckling instability due to the point loads on the bearings. In this way, a three dimensional finite element model (FEM) is built and the design of experiments technique (DOE) is applied to obtain the best stiffener configuration. The numerical simulation allows the exact definition of the response of the structure to be achieved, covering the gaps and limits which are common in some national and international codes. Very good results have been obtained, in terms of deflection, patch loading resistance and vertical load distribution on the support section. Finally, the most important conclusions of this work are given.

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